Published online 17 September 2009 | Nature | doi:10.1038/news.2009.926

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Volcanoes stirred by climate change

Impact of global warming on geological hazards 'poorly understood', experts warn.

VolcanoVolcanoes could erupt more violently in future if the planet warms.Getty

Geologists are desperately trying to gather data in an attempt to understand how global warming will affect violent geological activity.

As increasing atmospheric carbon dioxide levels warm the planet, the problems associated with melting ice won't just raise sea-levels; they will also uncap volcanoes. But just when and how these unstable magmatic beasts will blow in a warmer world is hard to predict.

"The fact is we are causing future contemporary climate change. [Geological hazards are] another portfolio of things we haven't thought of," says Bill McGuire from the Aon Benfield UCL Hazard Research Centre at University College London. He organized a meeting of volcanologists and oceanographers at the university on 15–17 September to draw attention to the problem.

On thin ice

A priority is to develop global models of how changes in the climate bring about changes in geological activity, and how those processes feed back into the system. At present, such models just don't exist, says David Pyle, a volcano expert from the University of Oxford, UK, who spoke at the meeting.

“As thick ice is getting thinner, there may be an increase in the explosivity of eruptions.”

Hugh Tuffen
Lancaster University

The problem is complex, exacerbated by the difficulty of separating forcing by the climate from the effects of a volcanic eruption — aerosols emitted by an eruption will have consequences for atmospheric chemistry, which in turn affect the climate. "The complex consequences of volcanic activity for the atmospheric biosphere remain poorly understood," Pyle says.

But there is definitely some evidence that less ice means more dramatic eruptions. "As thick ice is getting thinner, there may be an increase in the explosivity of eruptions," says Hugh Tuffen from Lancaster University, UK. Tuffen has spent time in many countries, including Iceland and Chile, studying volcanoes. The effects of climate change over the next 100 years will be different for different volcanoes, he says, and much more data are needed if we are to understand what those effects might be. But such data are not trivial to collect: volcanoes are isolated, dangerous places for field trips.

Data deficiencies

For example, in Iceland at the end of the last deglaciation period, about 11,000 years ago, there was a huge spike in volcanic activity that is now thought to be due to meltwater flooding the area. In Icelandic volcanoes, the ice provides a protective cap that, when removed, makes the magma below the surface decompress much faster than is already occurring through normal geological movement. The steady state that usually exists is lost, making eruptions faster and more explosive. There is not much delay between the climatic change and the volcanic eruption in these cases, says Tuffen.

But in the Andes the volcanoes are different. They have magma chambers beneath them. As the ice melts, again the protective cap is lost. This also looks to have caused an increase in volcanic activity in the past, but because the magma chambers are up to 5 kilometres deep, it is unclear just how quickly volcanism increased after the thaw, says Sebastian Watt, who works with Pyle at Oxford University.

Watt has collected data from 32 volcanic centres in Chile to try to come up with a more general trend for the acceleration of volcanic activity. He has used radiocarbon dating to work out the ages of various rock samples and from this has mapped when and where volcanoes across the spine of South America erupted over the past 18,000 years. Unfortunately, a geological cold snap has destroyed much of this evidence. "Dating is a problem; there is a shortage of radiocarbon data," says Watt.

Unclear threat

Tuffen warns that lives could be at risk. In Chile, at Nevados de Chillán, an area that seems particularly susceptible to climate change, local geologists were incensed, he says, when a ski resort was built close to a volcano.

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Tony Song from NASA's Jet Propulsion Laboratory in Pasadena, California, has modelled a hypothetical scenario in which melting could trigger a huge underground landslide, causing an enormous glacial tsunami. "As ice sheets melt more quickly than thought, these should be thought of more," says Song.

"We still don't really know what the threat over the next 100 years will be," says Tuffen. "I don't think we should be scaremongering, we should be thinking about hazard mitigation."

McGuire agrees. "The IPCC [Intergovernmental Panel on Climate Change] hasn't addressed these kinds of hazard," he says. "You have a better chance of coping with any kind of hazard if you know it's happening," he adds. "Climate change is not just the atmosphere and hydrosphere; it's the geosphere as well." 

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